Lubricating oil composition

ABSTRACT

A lubricant composition is disclosed which can largely reduce abrasion, can exhibit a low friction coefficient steadily, and has a high corrosion resistance in the lubrication of an iron-based sliding member. The lubricant composition includes a lubricant base oil, a 3,4,5-trihydroxybenzoic acid ester in an amount of 0.01 to 10 mass % relative to the total amount of the lubricant composition, and a detergent dispersant in an amount of 0.1 to 20 mass % relative to the total amount of the lubricant composition.

TECHNICAL FIELD

The present invention relates to a lubricating oil composition. In particular, the invention relates to a lubricating oil composition that is used as a lubricating oil for an internal combustion engine, as a lubricating oil for a driving system, or as a hydraulic oil.

BACKGROUND ART

In recent years, reduction in environmental load has become desirable in various fields. In particular, reduction of carbon dioxide (CO₂) emission is a task of pressing urgency, and efforts to conserve energy have been made in various domestic industries and transport industries including automobile transportation, as well as in general public consumption.

For example, in the automotive industry, the efficiency of gasoline engine has been improved by adopting lean-burn technology, direct-injection technology or the like in order to improve on fuel consumption and to reduce CO₂ emissions. On the other hand, use of a low-friction material for sliding members, or adoption of fuel-saving lubricating oils for internal combustion engines or for driving systems has been attempted in order to reduce friction in the engines. A three-way catalyst is normally equipped in an engine to purify the exhaust gas discharged from the engine. Since the three-way catalyst is poisoned by phosphorus components and hence the exhaust gas purification rate will decrease with time, a reduction of phosphorus content in the lubricating oil has been desired. However, a reduction of phosphorus content in the lubricating oil could cause the problem of poor wear resistance, seizure, or the like. In order to deal with this problem, the applicant proposed a lubricating oil for an internal combustion engine that contains a dimer acid diamide and molybdenum dithiocarbamate (MoDTC) (see Patent Document 1).

In the industrial machines, especially those which require a large amount of work energy such as injection molding machine, working machine, press machine, forging press machine and the like, a hydraulic system that can convert the pressurized energy of a hydraulic pump into kinetic energy (work energy) is widely used. Energy conservation has also been increasingly desired for such a hydraulic system. Therefore, a hydraulic fluid, which is a pressure medium in a hydraulic system, has also been subjected to energy-saving measures, and attempts have been made to reduce its viscosity or increase its viscosity index. However, a decrease in wear resistance of sliding members, seizure of sliding members, and so on, have been the problems associated with the lower viscosity.

In recent years, since the load imposed on the sliding members has been increasing as the machine systems become smaller, faster, more fuel-efficient, and more energy-saving, a lubricating oil that exhibits a superior lubricating property (e.g., wear resistance property, etc.) has been desired.

Ideal characteristics of a lubricating oil is that friction losses are small at high speed as well as at low speed, and that wear such as fretting wear or the like is small. In other words, a lubricating oil that reduces friction loss and wear is desired. Therefore, it is desirable that lubricating oil produces little friction loss and little wear even when the contact surface speed is high during high-speed rotation or when a high torque is applied at low speed.

It is necessary to reduce the viscosity of the lubricating oil base oil itself in order to reduce friction loss at high speed. However, wear due to fretting may easily occur when the viscosity of the lubricating oil base oil is reduced; that is, base metals of the sliding members could come into contact with each other, causing wear or seizure.

PRIOR ART DOCUMENT Patent Document

-   [Patent Document 1] JP-A-2008-37894

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

The inventors conducted extensive research in order to solve the above problems. As a result, the inventors surprisingly found that a 3,4,5-trihydroxybenzoic acid ester

(1) has a function of reducing the friction coefficient and inhibiting wear,

(2) exhibits a high rust prevention effect by reducing hematite (iron red rust) into magnetite (black rust) which is characterized by hardness and strength, and

(3) can exhibit the above effects when used in combination with a detergent dispersant, although 3,4,5-trihydroxybenzoic acid ester by itself has a low solubility to a mineral lubricating oil base oil and therefore without the detergent dispersant it would not exhibit the above effects. These findings have led to the completion of the invention.

The invention may solve various problems which occur on sliding members and which are becoming severer as a consequence of the smaller size, faster speed, better fuel efficiency and better energy-saving of the machine systems as mentioned above. An object of the invention is to provide a lubricating oil composition that significantly reduces wear, stably exhibits a low friction coefficient, and has a high rust prevention effect in lubrication of iron sliding members.

Means for Solving The Problems

Specifically, the present invention is as follows:

(1) A lubricating oil composition comprising a lubricating oil base oil, a 3,4,5-trihydroxybenzoic acid ester in an amount of 0.01 to 10 mass % relative to the total of the lubricating oil composition, and a detergent dispersant in an amount of 0.1 to 20 mass % relative to the total of the lubricating oil composition.

(2) The lubricating oil composition according to (1), wherein the 3,4,5-trihydroxybenzoic acid ester is a 3,4,5-trihydroxybenzoic acid alkyl ester synthesized from 3,4,5-trihydroxybenzoic acid and a linear or branched alcohol having 3 to 12 carbon atoms.

(3) The lubricating oil composition according to (1) or (2), wherein the lubricating oil base oil has a kinematic viscosity at 40° C. of 5 to 1000 mm²/s.

(4) A lubricating oil for an internal combustion engine, a lubricating oil for a driving system, or a hydraulic oil, comprising the lubricating oil composition according to any one of (1) to (3).

Effects of the Invention

Since the lubricating oil composition according to the invention comprises a lubricating oil base oil, a 3,4,5-trihydroxybenzoic acid ester, and a detergent dispersant, it significantly reduces wear, stably exhibits low friction coefficient, and has an excellent rust prevention effect on iron sliding members. Therefore, the lubricating oil composition of the invention can be suitable for a long-term use, and exhibit a significant effect for energy conservation due to the low and stable friction coefficient.

MODES FOR CARRYING OUT THE INVENTION

A lubricating oil composition according to the invention contains a 3,4,5-trihydroxybenzoic acid ester in an amount of 0.01 to 10 mass %, and a detergent dispersant in an amount of 0.1 to 20 mass %, in addition to a lubricating oil base oil. Since a 3,4,5-trihydroxybenzoic acid ester exhibits low solubility in a mineral base oil or in a hydrocarbon base oil not containing a polar group such as ester, ether or the like, the 3,4,5-trihydroxybenzoic acid ester alone cannot be added to the effective concentration at which the improved lubricity is achieved. However, the 3,4,5-trihydroxybenzoic acid ester can be used at the effective concentration at which the improved lubricity is achieved if it is used in combination with a detergent dispersant.

Lubricating Oil Base Oil

Mineral oil, synthetic oil, animal/plant oil, or the like may be used as the lubricating oil base oil in the invention. Two or more of these lubricating oil base oils may also be used in combination.

The physical properties of the lubricating oil base oil used in the lubricating oil composition according to the invention are not particularly limited, but it is preferable that the lubricating oil base oil has a kinematic viscosity at 40° C. of 5 to 1000 mm²/s, more preferably 5 to 500 mm²/s, and still more preferably 5 to 100 mm²/s, because the energy conservation can be facilitated by reducing the viscosity. However, it should be noted that, for high-load applications, it is preferable to use a base oil having high viscosity.

The viscosity index of the lubricating oil base oil is preferably 90 or higher, and more preferably 100 to 250. The pour point, which is a low-temperature property, of the lubricating oil base oil is preferably −10° C. or lower, and more preferably −15° C. or lower. Moreover, from the viewpoint of safety, the flash point of the lubricating oil base oil is preferably 70° C. or higher, and more preferably 150° C. or higher.

The lubricating oil base oil is preferably used in an amount of 70 to 99 mass % relative to the total amount of the lubricating oil composition, and more preferably 80 to 98 mass %.

As a mineral lubricating oil base oil, a purified lubricating oil base oil obtained by subjecting a lube oil fraction (which is obtained by distilling crude oil under atmospheric pressure or distilling the atmospheric residue under reduced pressure) to an appropriate combination of lubricating oil purification means, such as hydrocracking, solvent extraction, hydrorefining, solvent dewaxing, hydrodewaxing, clay treatment and the like, may be used. A mineral lubricating oil base oil obtained from a petroleum fraction having a relatively high boiling point is generally inexpensive, and thus has been widely used in various kinds of lubricating oils, greases, and the like. Therefore, from the economic point of view, it is preferable to use the mineral lubricating oil base oil alone as the base oil in the present invention.

Examples of synthetic lubricating oil base oil include poly-α-olefin (PAO), alkylbenzene, alkylnaphthalene, ester, ether, glycol, silicone oil, fluorinated oil, and the like. Among them, PAO and ester are preferable. PAO is chemically inert, exhibits excellent viscosity properties, and has a wide viscosity range that is commercially available, and is therefore conveniently used.

Various ester compounds having different molecular structures are commercially available, and each ester compound has unique characteristics. These ester compounds have higher flash points compared to the hydrocarbon base oils having equivalent viscosity. An ester may be obtained by dehydration condensation polymerization reaction of an alcohol and a fatty acid. It is preferable to use a diester of a dibasic acid and a monohydric alcohol or a polyol ester of a polyol and a monovalent fatty acid as the lubricating oil base oil in the invention from the viewpoint of chemical stability.

Examples of an animal/plant lubricating oil base oil preferably include, but are not limited to, milk (butter) fat, beef fat, lard, mutton tallow, nests foot oil, whale oil, salmon oil, bonito oil, herring oil, cod liver oil, as well as soybean oil, rape oil, sunflower oil, safflower oil, arachis oil, corn oil, cotton seed oil, rice bran oil, kapok oil, sesame oil, olive oil, linseed oil, castor oil, cacao butter, shea butter, palm oil, palm kernel oil, coconut oil, hempseed oil, rice oil, and tea seed oil.

The mineral lubricating oil base oil, the synthetic lubricating oil base oil, the animal/plant lubricating oil base oil, and the like may be formulated in appropriate combination and in an appropriate ratio so that the performance required for each application can be obtained. In these formulations, a plurality of mineral lubricating oil base oils, a plurality of synthetic lubricating oil base oils, and/or a plurality of animal/plant lubricating oil base oils may be used.

Since a 3,4,5-trihydroxybenzoic acid ester exhibits high solubility in a lubricating oil base oil having a polar group, such as synthetic ester or ether and animal/plant base oil, the amount of the detergent dispersant added can be reduced when such base oil is used. However, since such lubricating oil base oil having a polar group generally has low hydrolysis stability and is expensive, it is preferable to admix the lubricating oil base oil having a polar group in an amount of 50 parts by mass or less, and more preferably 5 to 30 parts by mass, relative to 100 parts by mass of a mineral lubricating oil base oil.

3,4,5-Trihydroxybenzoic acid ester

The 3,4,5-trihydroxybenzoic acid ester added in the lubricating oil composition according to the invention is preferably a 3,4,5-trihydroxybenzoic acid alkyl ester synthesized from 3,4,5-trihydroxybenzoic acid and a linear or branched alcohol having 3 to 12 carbon atoms. Among the 3,4,5-trihydroxybenzoic acid alkyl esters, a 3,4,5-trihydroxybenzoic acid propyl ester, 3,4,5-trihydroxybenzoic acid butyl ester, 3,4,5-trihydroxybenzoic acid hexyl ester, 3,4,5-trihydroxybenzoic acid octyl ester, 3,4,5-trihydroxybenzoic acid decyl ester, or 3,4,5-trihydroxybenzoic acid dodecyl ester is preferable. In particular a 3,4,5-trihydroxybenzoic acid propyl ester and 3,4,5-trihydroxybenzoic acid octyl ester are preferable from the viewpoint of the balance between solubility in the base oil and the lubricity improvement effect. The alkyl group may be linear or branched.

The 3,4,5-trihydroxybenzoic acid ester is added in an amount of 0.01 to 10 mass % relative to the total amount of the lubricating oil composition, and preferably 0.1 to 5 mass %. If the amount of the 3,4,5-trihydroxybenzoic acid ester is less than 0.01 mass %, reduction in wear, reduction in friction coefficient or prevention of rust may not be sufficiently achieved. If the amount of the 3,4,5-trihydroxybenzoic acid ester exceeds 10 mass %, a further improvement of the effects may not be expected in proportion to the additional amount, and therefore it is not economical.

Detergent Dispersant

Examples of the detergent dispersant preferably include metal detergents such as alkaline-earth metal sulfonates, alkaline-earth metal phenates, alkaline-earth metal salicylates and the like, and ashless dispersants such as polyalkenylsuccinimides, polyalkenylsuccinic acid esters, and boric acid-modified substances thereof or phosphonates thereof, benzylamines, boron-containing benzylamines, mono or dicarboxylic acid amides (e.g., typically fatty acid amide or succinic acid amide, respectively) and the like.

The alkaline-earth metal sulfonate is an alkaline-earth metal salt of a product obtained by sulfonating an alkyl aromatic compound using fuming sulfuric acid or sulfuric acid. The alkaline-earth metal phenate is an alkaline-earth metal salt of a Mannich reaction product of an alkylphenol sulfide or an alkylphenol obtained by reacting an alkylphenol sulfide with formaldehyde. The alkaline-earth metal salicylate is an alkaline-earth metal salt of an alkylsalicylic acid. Examples of the alkaline-earth metal forming the salt include calcium, barium, magnesium, and the like. Among them, calcium is particularly preferable. The metal salt is not limited to a neutral salt, and an overbased metal salt obtained by further adding an alkaline-earth metal salt may also be used.

As polyalkenylsuccinimide, ashless dispersants obtained by a reaction of polybutenylsuccinic acid polyamine obtained by maleation of polybutene having a molecular weight of 1000 to several thousands may preferably be used.

Although it may be difficult to strictly consider a detergent effect and a dispersant effect separately, in the present invention, it is speculated that the detergent dispersant plays a role of dissolving and dispersing the 3,4,5-trihydroxybenzoic acid ester (which has low solubility in a hydrocarbon oil) in the base oil.

The detergent dispersant is used in an amount of 0.1 to 20 mass % relative to the total amount of the lubricating oil composition, and preferably 1 to 10 mass %. If the amount of the detergent dispersant is less than 0.1 mass %, the effect obtained may be insufficient. On the other hand, if the amount of the detergent dispersant exceeds 20 mass %, a further improvement of the effects corresponding to the additional amount may not be expected, and it is therefore not economical.

Other Additives

The lubricating oil composition according to the invention may further comprise other additives that are conventionally used in a lubricating oil, grease, or the like, such as friction modifier, antiwear agent, extreme pressure agent, antioxidant, rust preventive, metal deactivator, anti-foaming agent and the like, in order to further improve the performance of the composition, provided that the effects of the invention are not impaired by the other additives.

Examples of the friction modifier include organomolybdenum compounds such as molybdenum dithiocarbamate and molybdenum dithiophosphate, nitrogen-containing compounds such as aliphatic amine, aliphatic amide and aliphatic imide, alcohols, esters, phosphate amine salts, phosphite amine salts, and the like. Examples of the antiwear agent include phosphates, zinc dialkyldithiophosphate, and the like. Examples of the extreme pressure agent include sulfurized olefins, sulfurized fats and oils, and the like. Examples of the antioxidant include amine antioxidants, phenol antioxidants, and the like. Examples of the metal deactivator include benzotriazoles and the like. Examples of the rust preventive include alkenylsuccinic acid esters or partial esters, and the like. Examples of the anti-foaming agent include silicone compounds, ester type anti-foaming agents, and the like.

The lubricating oil composition according to the invention may suitably be used as a lubricating oil for an internal combustion engine, a lubricating oil for a driving system, or a hydraulic oil.

EXAMPLES

The invention is further described below by way of examples and comparative examples. However, the invention is not limited to the following examples.

Preparation of Lubricating Oil Composition

A 3,4,5-trihydroxybenzoic acid ester, a lubricating oil base oil, a detergent dispersant, and an additive indicated below were blended in a ratio shown in Table 1 to prepare the lubricating oil compositions of Examples and Comparative Examples. For measuring the properties of the base oils and lubricating oils of Examples and Comparative Examples, the viscosity and the viscosity index were measured in accordance with JIS K 2283, the pour point was measured in accordance with JIS K 2269, and the flash point was measured in accordance with JIS K 2265-4.

(A) 3,4,5-trihydroxybenzoic acid ester

(A1) 3,4,5-trihydroxybenzoic acid propyl (n-propyl) ester (manufactured by Iwate Chemical Co., Ltd.)

(A2) 3,4,5-trihydroxybenzoic acid octyl (n-octyl) ester (manufactured by Wako Pure Chemical Industries, Ltd.)

(B) Lubricating Oil Base Oil

(B1) Paraffinic mineral oil (kinematic viscosity (40° C.): 32 mm²/s, viscosity index: 106, pour point: −15° C., flash point: 230° C.)

(B2) Polyol ester oil (kinematic viscosity (40° C.): 10 mm²/s, viscosity index: 95, pour point: −50° C., flash point: 190° C.)

(B3) Poly-α-olefin (PAO) (kinematic viscosity (40° C.): 400 mm²/s, viscosity index: 150, pour point: −35° C., flash point: 280° C.)

(C) Detergent Dispersant

(C1) Neutral calcium sulfonate

(C2) Polybutenylsuccinimide

(D) Other Additive

(D1) Antioxidant: di-t-butyl-p-cresol (DBPC)

(D2) Antiwear agent: tricresyl phosphate (TCP)

(D3) Friction modifier: molybdenum dithiocarbamate (MoDTC)

Each lubricating oil composition of Examples 1 to 7 and Comparative Examples 1 to 4 obtained in the above manner was evaluated for its appearance and lubricity (friction coefficient and wear depth) by the standard commonly applied to lubricating oil compositions.

Measurement Methods and Evaluation Methods

The measurement and evaluation were carried out in accordance with the following methods.

Appearance

The composition prepared by blending the components in the ratio shown in Table 1 was cooled to room temperature, and the appearance of the resulting composition was observed with the naked eye. A case where a precipitate or deposit had been formed was judged as “Bad”, and a case where a homogeneous liquid had been obtained was judged as “Good”.

Wear Resistant Test

The wear resistance of the lubricating oil compositions of Examples 1 to 7 and Comparative Examples 1 to 4 was measured using a ball-on-disk reciprocating friction tester.

A low sliding speed (1 cm/s) and a high load (2200 gf) were selected so that the test was carried out under a condition where an oil film could not easily form, i.e., under a severe lubricating condition. The test was started at room temperature at an amplitude of 20 mm. A reciprocating friction operation was performed for 2 hours. Bearing carbon steel (SUJ-2) was used as test pieces of the ball and the disk. The friction coefficient after 2 hours of elapsed time and the disk wear depth after the test were measured using a contact surface roughness tester.

Next, the properties of the lubricant compositions of Examples 1 to 7 as a lubricating oil for an internal combustion engine, as a lubricating oil for driving system, and as a hydraulic oil were evaluated, and compared with those of the lubricating oil compositions of Comparative Examples 1 to 4.

Evaluation as Lubricating Oil for Internal Combustion Engine

The lubricating oil for an internal combustion engine was evaluated by measuring the disk wear scar diameter and the friction coefficient at a high temperature of 100° C. using a cylinder/disk SRV friction tester.

The test was conducted by applying a reciprocating friction to the disk using the cylinder under the following conditions: a load of 200 N, a frequency of 300 Hz, an amplitude of 1.0 mm, and test time of 1 hour, and diameter of the wear scar formed on the disk was measured using a microscope. The friction coefficient was measured using a strain gauge which was pre-equipped on the friction tester.

Evaluation as Lubricating Oil for Driving System

The lubricating oil for a driving system was evaluated using an FZG pitting test. The test was performed in accordance with DIN 51354 by using a TYPE PTC gear under the following conditions: a load of 9 stage, an oil temperature of 120° C., and a rotational speed of 1440 per minute. The fatigue life was defined as the time (hr) at which a pitting having a size of 1 mm² had occurred, and determined by stopping the test device at regular intervals and inspecting the tooth surface each time. The tooth surface was inspected every 8 hours during the initial 24 hours, and every 2 to 4 hours thereafter.

Evaluation as Hydraulic Oil

The lubricating oil composition as a hydraulic oil was evaluated using a high-pressure vane pump test. The high-pressure vane pump test was performed in accordance with ASTM D2882. 56.8 liters of the oil was circulated in the pump test instrument under the following conditions: a pressure of 140 kg/cm², a pump speed of 1200 rpm, and an inlet oil temperature of 65.5° C., for 100 hours. Subsequently the reduction in the total weight of the vane and the cam ring was measured, and taken as the amount of wear.

The measurement/evaluation results are collectively shown in Table 1.

TABLE 1 Example Comparative Example 1 2 3 4 5 6 7 1 2 3 4 Component 3,4,5-Trihydroxybenzoic [mass %] acid compound A1 (3,4,5-trihydroxy- 0.1 0.5 — 0.5 0.5 0.1 — 0.5 — — — benzoic acid propyl ester) A2 (3,4,5-trihydroxy- — — 5.0 — — — 1.0 — — — — benzoic octyl ester) Base oil B1 (mineral oil) 89.7 89.3 89.8 — — 90.0 80.0 99.3 89.8 — — B2 (polyol ester) — — — 98.3 — 7.7 15.8 — — 98.8 — B3 (PAO) — — — — 88.3 — — — — — 92.8 Detergent dispersant C1 (Ca sulfonate) 10.0 10.0 — 1.0 — 1.0 — — 10.0 — — C2 (succinimide) — — 5.0 — 10.0 — 1.0 — — 5.0 Additive C1 (DBPC) 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 C2 (TCP) — — — — 1.0 — 1.0 — — 1.0 1.0 C3 (MoDTC) — — — — — 1.0 1.0 — — — 1.0 Property Kinematic viscosity 31 31 30 10 392 29 27 32 32 10 396 (40° C.) [mm²/s] Viscosity index 105 105 105 95 147 104 103 105 105 95 148 Pour point [° C.] −15 −15 −15 −50 −35 −17.5 −22.5 −15 −15 −50 −35 Basic Appearance Good Good Good Good Good Good Good Bad Good Good Good Performance Wear resistance test (turbid) Coefficient of friction 0.07 0.06 0.05 0.06 0.06 0.05 0.05 0.12 0.16 0.13 0.13 0.06 0.05 0.04 0.06 0.05 0.05 0.04 0.38 1.04 0.62 0.54 Wear depth [μm] Performance SRV friction test (100° C.) Friction coefficient 0.08 0.07 0.07 0.07 0.07 0.06 0.06 0.13 0.16 0.15 0.12 Wear scar diameter [mm] 0.39 0.36 0.33 0.30 0.33 0.29 0.31 0.51 0.61 0.58 0.56 FZG pitting test [hr] 68 72 78 72 72 78 78 42 30 32 32 High-pressure vane pump test Wear amount [mg] 36 35 28 30 31 25 24 58 114 92 84

The lubricating oil compositions of Examples 1 to 7 were all homogenous liquids. The friction coefficients of these Examples were 0.05 to 0.07 and thus consistently low. The disks were hardly worn in the Examples, having the wear depths of 0.04 to 0.06 μm.

In contrast, the composition of Comparative Example 1 that contained 3,4,5-trihydroxybenzoic acid propyl ester but not a detergent dispersant had a turbid appearance, indicating that 3,4,5-trihydroxybenzoic acid propyl ester was not uniformly dissolved or dispersed. Accordingly, the friction coefficient was high and the disk wear depth was large. The compositions of Comparative Examples 2 to 4 that did not contain a 3,4,5-trihydroxybenzoic acid ester had a high friction coefficient, and the disk wear depths thereof were far larger than those of the compositions of Examples.

It was thus confirmed that the lubricity of a lubricating oil composition can be significantly improved by blending a 3,4,5-trihydroxybenzoic acid ester and a detergent dispersant with a lubricating oil base oil.

Furthermore, the lubricating oil compositions of Examples 1 to 7 all exhibited excellent properties as a lubricating oil for an internal combustion engine, as a lubricating oil for a driving system, and as a hydraulic oil.

INDUSTRIAL APPLICABILITY

Since the lubricating oil composition according to the invention significantly reduces wear, has a low and stable friction coefficient, and exhibits an excellent rust prevention effect on iron sliding members, the lubricating oil composition may be useful as a lubricating oil for sliding members of various machines and instruments, in particular as a lubricating oil for an internal combustion engine, a lubricating oil for a driving system or a hydraulic oil. 

1. A lubricating oil composition comprising a lubricating oil base oil, a 3,4,5-trihydroxybenzoic acid ester in an amount of 0.01 to 10 mass % relative to the total of the lubricating oil composition, and a detergent dispersant in an amount of 0.1 to 20 mass % relative to the total of the lubricating oil composition.
 2. The lubricating oil composition according to claim 1, wherein the 3,4,5-trihydroxybenzoic acid ester is a 3,4,5-trihydroxybenzoic acid alkyl ester synthesized from 3,4,5-trihydroxybenzoic acid and a linear or branched alcohol having 3 to 12 carbon atoms.
 3. The lubricating oil composition according to claim 1, wherein the lubricating oil base oil has a kinematic viscosity at 40° C. of 5 to 1000 mm²/s.
 4. A lubricating oil for an internal combustion engine, a lubricating oil for a driving system, or a hydraulic oil, comprising the lubricating oil composition according to claim
 1. 5. The lubricating oil composition according to claim 2, wherein the lubricating oil base oil has a kinematic viscosity at 40° C. of 5 to 1000 mm²/s.
 6. A lubricating oil for an internal combustion engine, a lubricating oil for a driving system, or a hydraulic oil, comprising the lubricating oil composition according to claim
 2. 7. A lubricating oil for an internal combustion engine, a lubricating oil for a driving system, or a hydraulic oil, comprising the lubricating oil composition according to claim
 3. 8. A lubricating oil for an internal combustion engine, a lubricating oil for a driving system, or a hydraulic oil, comprising the lubricating oil composition according to claim
 5. 